Immanuel Kant was a transformative figure in modern Western philosophy due to his ground-breaking work in metaphysics and ethics.

He was one of the most influential philosophers of the 18th century, and his work in metaphysics and ethics have had a lasting impact to this day.

One of Kant’s greatest contributions to philosophy was his moral theory, deontology, which judges actions according to whether they adhere to a valid rule rather than the outcome of the action.

According to Kant’s theory, if you follow a valid moral rule, like “do not lie”, and it ends up with people getting harmed, then you’ve still done the right thing.

Deontology has since become one of the “big three” moral frameworks in the Western tradition, along with virtue ethics (based on Aristotle’s work) and consequentialism (exemplified by utilitarianism).

The will

Kant argued that morality cannot be based on our emotions or experience of the world, because this would leave it weak and subjective, and lacking the unconditional obligation that he believed was central to moral law.

“Every one must admit that a law has to carry with it absolute necessity if it is to be valid morally – valid, that is, as a ground of obligation,” he wrote.

His concern was that without this sense of unconditional obligation, a moral rule like ‘do not lie’ could compete with and be overridden by other concerns, like someone deciding they could lie because it suits their interests to do so, and they value their interests more than morality.

Rather, Kant argued that morality must be based on reason, which alone can provide the unconditional necessity that makes morality override our subjective interests.

Kant’s starting point was with our very nature, as inherently rational beings with ‘free will.’ He argued that it was this will that sets us apart as ’persons’ rather than ’things’  in the world, which are at the mercy of causal forces.

Our will gives us the ability to not only decide how to achieve our ends, but also about which ends to pursue; that’s just what freedom means. However, Kant argued that when we understand our nature as rational beings, we will understand that reason commands us to behave in a certain way, and this could form the basis of objective moral law.

The Categorical Imperative

Kant drew a famous distinction between different types of commands, or imperatives, which direct us how to act. One type are hypothetical imperatives.

So, one hypothetical imperative might say if you want to get to the 5:05 PM bus on time, then you must leave home no later than 5 p.m. Many moral systems of his time were effectively based on hypothetical imperatives, with the ends being things like achieving happiness or satisfying our interests.

However, Kant believed that such hypothetical imperatives could not be the basis of morality, as morality must bind us to act unconditionally and irrespective of any other ends we might have. Hence, someone who followed hypothetical imperatives in order to achieve ends like satisfying their desires or to avoid punishment was not acting morally.

He contrasted these with categorical imperatives   do bind us unconditionally, no matter what other ends we might have. Kant argued that morality must be made up of categorical imperatives, as these are the only rules that can give morality its unconditional necessity.

“If duty is a concept which is to have meaning and real legislative authority for our actions, this can be expressed only in categorical imperatives and by no means in hypothetical ones,” he wrote.

The question becomes: where do categorical imperatives come from? Kant argued that there is really only one categorical imperative, and it is derived from our very nature as rational agents.


Once we abstract away all the contingent circumstances and subjective desires that people have, all we’re left with is our rational nature, which is something shared by all persons with a will. This objective point of view, stripped of all subjectivity, treats all rational agents equally, thus any imperative that directs them must apply universally.

From this Kant arrived at the categorical imperative, which is usually stated as “act only according to a maxim by which you can at the same time will that it shall become a general law”. This made all moral commands universal, so if something was wrong for me, then it must be wrong for all rational beings at all times.

This categorical imperative became the basis of all of Kant’s moral laws, effectively enshrining a particularly rarefied version of the Golden Rule.

Kingdom of Ends

Because we are inherently rational agents, we are both the authors and the subjects of the moral law. As such, Kant said that every person – indeed, every rational being – is an “end in himself, not merely as a means for arbitrary use by this or that will”.

This means we must treat all rational beings as ends in themselves and not just as means to achieve whatever ends we might have.

So, Kant argued, if every rational agent were to obey the categorical imperative, and treat everyone else as ends and not means, then it would lead to what he called the “kingdom of ends.”

It’s a kingdom in the sense that it’s a union of individuals who are all acting under a common law, and in this case the law is the categorical imperative, which urges everyone to treat everyone else as an end in themselves.

Kant admitted that this would be something of a moral utopia, but he put it forward as a vision for what a truly rational moral society might look like.

Controversy and Influence

Kant’s deontological ethics has been hugely influential but also controversial, being criticised by many philosophers as being based on an unrealistic conception of human rationality as well as being overly inflexible.

For example, Kant argued that it was always wrong to lie, because if one were to lie it would effectively endorse lying for everyone, and this would violate people’s rational autonomy.

However, we can imagine some situations where lying might be considered to be the right thing to do, such as lying to a prospective murderer in order to conceal their potential victims. Not to mention lying to one’s partner about their sartorial choices in order to maintain a harmonious domestic environment.

This is why many ethical consequentialists, who believe that it’s outcomes that really matter, have been known to gnash their teeth at the prospect that Kant demands we never lie.

Some thinkers have also – perhaps uncharitably – said that Kant effectively remade a kind of divine command theory of morality, which was popular in his Lutheran Christian community, except he replaced God with Reason (and even then, snuck a bit of God in on the side).

Kant’s philosophy has proven to be tremendously influential. His synthesis of empiricism and rationalism proved to be a breakthrough at the time, and his moral theory still has ardent defenders to this day.

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Can morality be based on our own emotions or experiences of the world?